Industrial tools for cutting and shaping materials are fabricated from hard materials in order to maintain their edges and to withstand the concentrated stresses that are present at the cutting edge. These tools are frequently fabricated from materials including high speed steel (HSS), cemented carbide, ceramic, polycrystalline diamond (PCD), polycrystalline cubic boron nitride (PCBN) or similar ultra-hard materials.
Investigations have found that imparting a small radius on the cutting edge of an industrial tool on the order of several micrometers has various advantages. A tool with an edge appropriately prepared is typically less susceptible to catastrophic chipping during machining, which leads to a manyfold improvement in tool life. In addition, edge preparation improves the overall surface quality of the machined parts. The process of imparting a very small radius on the cutting edge of a cutting tool is known as edge honing. Due to the aforementioned advantages, edge honing has become a critical element in the manufacture and performance of industrial cutting tools.
A variety of different devices and methods have been developed to hone the edges of cutting tools. U.S. Pat. No. 5,178,645 to Nakamura, et al. discloses a method for honing the edge of a PCD cutting tool by applying a YAG laser to the cutting edge of the tool. The tool is inclined with respect to the laser beam and moved to hone the cutting edge. Alternatively, the laser beam is adjusted while the tool is in a fixed position. The laser beam processing parameters are pre-selected such that a radius forms along the exposed portion of the cutting edge.
The method of U.S. Pat. No. 5,709,587 to Shaffer consists of directing a pressurized fluid stream that is comprised of an abrasive grit entrained in a fluid. The fluid stream is directed against the sharp cutting edge of an elongated rotary tool for a pre-selected time to transform the sharp cutting edge into a relatively honed edge.
The apparatus of U.S. Pat. No. 6,287,177 to Shaffer comprises a base with a rotating brush with abrasive bristles mounted to a variable speed motor. A mount with a fixture for holding the cutting tool is attached to the base. The mount has a translational mechanism for controlling the position of the edge of the cutting tool relative to the rotating brush. The edge of the cutting tool is honed by controlling the movement and position of the cutting tool through the volume of the abrasive bristles, which results in the formation of a tapered edge.
The method of U.S. Pat. No. 7,063,594 to Engin, et al. consists of immersing the cutting edges of a cutting tool in an abrasive liquid bath. The bath contains an abrasive granular media, which is circulated through the bath such that the cutting edges are disposed within the flow path of the abrasive media. Alternatively, the cutting edges of a cutting tool are immersed in an abrasive liquid bath and the cutting tool is rotated. The abrasive media is comprised of very small abrasive granules such that a radius along the full length of the cutting edges forms after prolonged exposure.
It is very difficult with the foregoing approaches to achieve a consistent and repeatable radius along the full length of the cutting edge. Variation in the edge radius affects cutting performance in terms of efficient chip formation, which has adverse implications in terms of tool life and the quality of the machined surface.
In addition to problems with generating consistent hone radii, these methods are also expensive, and are limited when applied to ultra-hard tool materials like such as PCD or PCBN, on account of their extreme hardness. The demand for such tools is on the rise, and hence the need for better honing methods.
Accordingly, an improved process for honing the edges of cutting tools with consistent and repeatable results is highly desired.